There are a variety of medical procedures that require light or irradiated energy to be administered to a columnar environment within the body of a patient, such as the esophagus. One example is therapeutic methods that use a light activated compound to selectively killing target cells in a patient, termed photoactivated chemotherapy. Other examples include optical diagnostic methods, hypothermia treatment and biostimulation.
In photoactivated chemotherapeutic methods, a light-sensitive drug is injected into a patient and a targeted light source is used to selectively activate the light-sensitive drug. When activated by light of a proper wavelength, the light-sensitive drug produces a cytotoxic agent that mediates the destruction of the surrounding cells or tissue.
The main application of photoactivated therapy, such as PDT, is for the destruction of malignant cell masses and precancerous cells. Photoactivated therapy has been used effectively in the treatment of a variety of human tumors and precancerous conditions including basal and squamous cells, skin cancers, breast cancer, metastatic to skin, brain tumors, head and neck, stomach, and female genital tract malignancy, cancers and precancerous conditions of the esophagus such as Barrett's esophagus. A review of the history and progress of photoactivated therapy is provided by Marcus, S. Photodynamic Therapy of Human Cancer: Clinical Status, Potential, and Needs. In Gomer, C. J. (ed.); "Future Directions and Applications in Photodynamic Therapy." Bellingham, W. A. SPIE Optical Engineering Press (1990) pp. 5-56 and specific applications of PDT are provided by Overholt et al., Sem. Surg. Oncol. 11:1-5 (1995).
One area of focus in the development of phototherapeutic methods and apparatus is the development of targeted light sources that provide uniform illumination to a given treatment area and their use in columnar environments.
Allardice et al. Gastrointestinal Endoscopy 35:548-551 (1989) and Rowland et al. PCT application WO 90/00914, disclose one type of light delivery systems designed for use with PDT. The disclosed system involves a flexible tube comprising a dilator and a transparent treatment window. A fiber optic element that is connected to a laser and ends in a diffusing tip is used in combination with the dilator to deliver light to a tissue source. Allardice et al. suggests using a 3 cm long, 1 cm in diameter treatment window for treating a 4 cm long region.
Nseyo et al. Urology 36:398-402 (1990) and Lundahl, U.S. Pat. Nos. 4,998,930 and 5,125,925, disclose a spherical balloon catheter device with a radius of 3.7 cm for providing uniform irradiation to the inner walls of hollow organs, such as the bladder.
Panjehpour et al. Lasers and Surgery in Medicine 12:631-638 (1992) discloses the use of a centering balloon catheter to improve esophageal photodynamic therapy. Panjehpour discloses a cylindrical balloon catheter, having a cylindrical treatment window 3.6 cm long, into which a fiber optic probe ending in a light diffuser is inserted. The cylindrical balloon was used to deliver three treatments to the esophagus of a dog in a typical study. To treat the entire length of the column requiring treatment, the balloon was advanced into the column while multiple light doses were administered.
Overholt et al. Lasers and Surgery in Medicine 14:27-33 (1994) discloses modified forms of the balloon catheter device described by Panjehpour. The cylindrical balloon catheter was modified by coating both ends of the balloon with a black opaque coating to define a 360 degree treatment window of 2.0 to 2.6 cm in length.
Overholt et al. Gastrointestinal Endoscopy 42:64-70 (1995) discloses the use of Overholt (1994) balloon catheters for treating Barrett's esophagus. Overholt used treatment windows of 2 to 3 cm in length. Overholt used treatment windows of 2 cm to treat 4 to 7 cm area using multiple light doses while advancing the catheter into the esophagus during a typical treatment regime.
Overholt et al. Seminars in Surgical Onc. 11:1-5 (1995) discloses the clinical results of treating 12 patients with Barrett's esophagus using an Overholt (1994) balloon catheter. 2 to 3 cm in length treatment windows were used. Overholt suggests using a balloon catheter with a 2-3 cm treatment window and restricting the treatment length to 5 to 7 cm in a single treatment, even for patients requiring 6 to 10 cm in treatment.
Rowland et al. PCT application WO 90/00420, discloses a light-delivery system for irradiating a surface. The device comprises a hemispherical shell whose inside is entirely coated with a diffuse reflector and a light source that is mounted within the shell. The light source may contain a diffusing source at the tip allowing diffusion of light within the reflective shell.
Spears, U.S. Pat. No. 5,344,419, discloses apparatuses and methods for making laser-balloon catheters. Spears utilizes a process that etches an end of a fiber optic cable to provide a diffusion tip on the optical cable. The optical cable containing the etched tip is secured within a central channel of a balloon catheter using a coating of adhesive containing microballoons. The position of the tip within the central channel and the microballoons contained in the adhesive provide increased efficiency in diffusing the laser radiation in a cylindrical pattern, providing a more uniform illumination at the target site.
Beyer, et al. U.S. Pat. No. 5,354,293 discloses a spherical balloon catheter apparatus for delivering light for use in PDT. The balloon catheter device disclosed employs a conical tipped fiber optic cable to provide means of deflecting a light beam radially outward through a transparent portion of an inflated catheter of 2 cm in diameter.
In summary, there have been numerous devices that have been developed for use in PDT that employ a balloon catheter to support a light source in an ideal central point within a target area that is to be illuminated (Spears, Overholt, Beyer, Lundahl and Allardice) The main benefits of using a centering type balloon are that 1) the clinician does not have to hold the fiber optic in the central location, this is done automatically by the balloon catheter, 2) the light dose is more uniform across the entire treatment area than would be the case of light delivered by a fiber optic that is held central to the treatment volume without the aid of a balloon (while this is true with existing designs of balloon catheters, it is herein demonstrated that the uniformity can be significantly improved), 3) the treatment field is kept clean of contaminants e.g. blood, urine that might absorb the light and so effect the final PDT result, and 4) the overall treatment procedure can be considerably shortened as it is simpler setting up the fiber optic and getting the light dose correct.
Although teaching the use of balloon catheters to provide light to columnar environments, each of the above references that discloses such uses and devices suggest using irradiation segments of 3 cm or less when treating columnar environments such as the esophagus, even when the required treatment length may be longer than 7 cm. The various authors suggest using multiple light doses, each time advancing the light element farther into the columnar environment. The various authors further suggest that treatment lengths be limited to 5 to 7 cm for a particular treatment session.